We analyze Einsteins recoiling slit experiment and point out that the inevitable entanglement between the particle and the recoiling-slit was not part of Bohrs reply. We show that if this entanglement is taken into account, one can provided a simpler
answer to Einstein. We also derive the Englert-Greenberger-Yasin duality relation from this entanglement. In addition, we show that the Englert-Greenberger-Yasin duality relation can also be thought of as a consequence of the sum uncertainty relation for certain observables of the recoiling slit. Thus, the uncertainty relations and entanglement are both an integral part of the which-way detection process.
